Wet Spinning of Chitosan Fibers: Effect of Sodium Dodecyl Sulfate Adsorption and Enhanced Dope Temperature

Production of fibers from nonthermoplastic polymers, such as chitosan, usually requires dissolution with subsequent fiber formation, for instance, via coagulation. Good fiber-forming properties enable simultaneous spinning of multiple fibers into a yarn, which is one of the prerequisites for process scalability. Here, we report a multifilament wet-spinning process that eliminates the use of such volatile organic compounds as methanol and acetone, enhances fiber formation, and allows producing continuous well-separated chitosan fibers after drying. This is achieved by (i) solidification of the extruded solution by alkali and sodium acetate in the coagulation bath and (ii) further stabilization of the fibers by adsorbing the anionic surfactant, sodium dodecyl sulfate. The obtained fibers have a circular cross section and smooth surface. We demonstrate that it is possible to increase fiber breaking tenacity and Young's modulus by applying stretching (draw ratios up to 1.77) or by incorporating cellulose nanofibrils (CNFs, up to 4 wt % based on chitosan) in the spinning solutions. However, the limitation of increased viscosity when adding CNF is needed to be overcome for possible higher reinforcement effects. We demonstrate that fiber breaking tenacity, Young's modulus, and elongation at break can be enhanced even further by increasing the spin dope temperature from 22 to 60 °C, with simultaneously increasing the spin dope solid content to keep the same dope viscosity. The fibers with a maximum breaking tenacity of ca. 10 cN/tex at an elongation at break of ca. 7.5% were obtained.